/* * Read-Copy Update mechanism for mutual exclusion * * This program is free software; you can redistribute it and/or modify * it under the terms of the GNU General Public License as published by * the Free Software Foundation; either version 2 of the License, or * (at your option) any later version. * * This program is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the * GNU General Public License for more details. * * You should have received a copy of the GNU General Public License * along with this program; if not, write to the Free Software * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. * * Copyright IBM Corporation, 2001 * * Author: Dipankar Sarma * * Based on the original work by Paul McKenney * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen. * Papers: * http://www.rdrop.com/users/paulmck/paper/rclockpdcsproof.pdf * http://lse.sourceforge.net/locking/rclock_OLS.2001.05.01c.sc.pdf (OLS2001) * * For detailed explanation of Read-Copy Update mechanism see - * http://lse.sourceforge.net/locking/rcupdate.html * */ #ifndef __LINUX_RCUPDATE_H #define __LINUX_RCUPDATE_H #include #include #include #include #include #include #include #ifdef CONFIG_RCU_TORTURE_TEST extern int rcutorture_runnable; /* for sysctl */ #endif /* #ifdef CONFIG_RCU_TORTURE_TEST */ /** * struct rcu_head - callback structure for use with RCU * @next: next update requests in a list * @func: actual update function to call after the grace period. */ struct rcu_head { struct rcu_head *next; void (*func)(struct rcu_head *head); }; /* Exported common interfaces */ extern void synchronize_rcu_bh(void); extern void synchronize_sched(void); extern void rcu_barrier(void); extern void rcu_barrier_bh(void); extern void rcu_barrier_sched(void); extern void synchronize_sched_expedited(void); extern int sched_expedited_torture_stats(char *page); /* Internal to kernel */ extern void rcu_init(void); extern int rcu_scheduler_active; extern void rcu_scheduler_starting(void); #if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU) #include #elif defined(CONFIG_TINY_RCU) #include #else #error "Unknown RCU implementation specified to kernel configuration" #endif #define RCU_HEAD_INIT { .next = NULL, .func = NULL } #define RCU_HEAD(head) struct rcu_head head = RCU_HEAD_INIT #define INIT_RCU_HEAD(ptr) do { \ (ptr)->next = NULL; (ptr)->func = NULL; \ } while (0) #ifdef CONFIG_DEBUG_LOCK_ALLOC extern struct lockdep_map rcu_lock_map; # define rcu_read_acquire() \ lock_acquire(&rcu_lock_map, 0, 0, 2, 1, NULL, _THIS_IP_) # define rcu_read_release() lock_release(&rcu_lock_map, 1, _THIS_IP_) extern struct lockdep_map rcu_bh_lock_map; # define rcu_read_acquire_bh() \ lock_acquire(&rcu_bh_lock_map, 0, 0, 2, 1, NULL, _THIS_IP_) # define rcu_read_release_bh() lock_release(&rcu_bh_lock_map, 1, _THIS_IP_) extern struct lockdep_map rcu_sched_lock_map; # define rcu_read_acquire_sched() \ lock_acquire(&rcu_sched_lock_map, 0, 0, 2, 1, NULL, _THIS_IP_) # define rcu_read_release_sched() \ lock_release(&rcu_sched_lock_map, 1, _THIS_IP_) extern int debug_lockdep_rcu_enabled(void); /** * rcu_read_lock_held - might we be in RCU read-side critical section? * * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an RCU * read-side critical section. In absence of CONFIG_DEBUG_LOCK_ALLOC, * this assumes we are in an RCU read-side critical section unless it can * prove otherwise. * * Check rcu_scheduler_active to prevent false positives during boot. */ static inline int rcu_read_lock_held(void) { if (!debug_lockdep_rcu_enabled()) return 1; return lock_is_held(&rcu_lock_map); } /* * rcu_read_lock_bh_held() is defined out of line to avoid #include-file * hell. */ extern int rcu_read_lock_bh_held(void); /** * rcu_read_lock_sched_held - might we be in RCU-sched read-side critical section? * * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an * RCU-sched read-side critical section. In absence of * CONFIG_DEBUG_LOCK_ALLOC, this assumes we are in an RCU-sched read-side * critical section unless it can prove otherwise. Note that disabling * of preemption (including disabling irqs) counts as an RCU-sched * read-side critical section. * * Check rcu_scheduler_active to prevent false positives during boot. */ #ifdef CONFIG_PREEMPT static inline int rcu_read_lock_sched_held(void) { int lockdep_opinion = 0; if (!debug_lockdep_rcu_enabled()) return 1; if (debug_locks) lockdep_opinion = lock_is_held(&rcu_sched_lock_map); return lockdep_opinion || preempt_count() != 0 || irqs_disabled(); } #else /* #ifdef CONFIG_PREEMPT */ static inline int rcu_read_lock_sched_held(void) { return 1; } #endif /* #else #ifdef CONFIG_PREEMPT */ #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */ # define rcu_read_acquire() do { } while (0) # define rcu_read_release() do { } while (0) # define rcu_read_acquire_bh() do { } while (0) # define rcu_read_release_bh() do { } while (0) # define rcu_read_acquire_sched() do { } while (0) # define rcu_read_release_sched() do { } while (0) static inline int rcu_read_lock_held(void) { return 1; } static inline int rcu_read_lock_bh_held(void) { return 1; } #ifdef CONFIG_PREEMPT static inline int rcu_read_lock_sched_held(void) { return !rcu_scheduler_active || preempt_count() != 0 || irqs_disabled(); } #else /* #ifdef CONFIG_PREEMPT */ static inline int rcu_read_lock_sched_held(void) { return 1; } #endif /* #else #ifdef CONFIG_PREEMPT */ #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */ #ifdef CONFIG_PROVE_RCU extern int rcu_my_thread_group_empty(void); #define __do_rcu_dereference_check(c) \ do { \ static bool __warned; \ if (debug_lockdep_rcu_enabled() && !__warned && !(c)) { \ __warned = true; \ lockdep_rcu_dereference(__FILE__, __LINE__); \ } \ } while (0) /** * rcu_dereference_check - rcu_dereference with debug checking * @p: The pointer to read, prior to dereferencing * @c: The conditions under which the dereference will take place * * Do an rcu_dereference(), but check that the conditions under which the * dereference will take place are correct. Typically the conditions indicate * the various locking conditions that should be held at that point. The check * should return true if the conditions are satisfied. * * For example: * * bar = rcu_dereference_check(foo->bar, rcu_read_lock_held() || * lockdep_is_held(&foo->lock)); * * could be used to indicate to lockdep that foo->bar may only be dereferenced * if either the RCU read lock is held, or that the lock required to replace * the bar struct at foo->bar is held. * * Note that the list of conditions may also include indications of when a lock * need not be held, for example during initialisation or destruction of the * target struct: * * bar = rcu_dereference_check(foo->bar, rcu_read_lock_held() || * lockdep_is_held(&foo->lock) || * atomic_read(&foo->usage) == 0); */ #define rcu_dereference_check(p, c) \ ({ \ __do_rcu_dereference_check(c); \ rcu_dereference_raw(p); \ }) /** * rcu_dereference_protected - fetch RCU pointer when updates prevented * * Return the value of the specified RCU-protected pointer, but omit * both the smp_read_barrier_depends() and the ACCESS_ONCE(). This * is useful in cases where update-side locks prevent the value of the * pointer from changing. Please note that this primitive does -not- * prevent the compiler from repeating this reference or combining it * with other references, so it should not be used without protection * of appropriate locks. */ #define rcu_dereference_protected(p, c) \ ({ \ __do_rcu_dereference_check(c); \ (p); \ }) #else /* #ifdef CONFIG_PROVE_RCU */ #define rcu_dereference_check(p, c) rcu_dereference_raw(p) #define rcu_dereference_protected(p, c) (p) #endif /* #else #ifdef CONFIG_PROVE_RCU */ /** * rcu_access_pointer - fetch RCU pointer with no dereferencing * * Return the value of the specified RCU-protected pointer, but omit the * smp_read_barrier_depends() and keep the ACCESS_ONCE(). This is useful * when the value of this pointer is accessed, but the pointer is not * dereferenced, for example, when testing an RCU-protected pointer against * NULL. This may also be used in cases where update-side locks prevent * the value of the pointer from changing, but rcu_dereference_protected() * is a lighter-weight primitive for this use case. */ #define rcu_access_pointer(p) ACCESS_ONCE(p) /** * rcu_read_lock - mark the beginning of an RCU read-side critical section. * * When synchronize_rcu() is invoked on one CPU while other CPUs * are within RCU read-side critical sections, then the * synchronize_rcu() is guaranteed to block until after all the other * CPUs exit their critical sections. Similarly, if call_rcu() is invoked * on one CPU while other CPUs are within RCU read-side critical * sections, invocation of the corresponding RCU callback is deferred * until after the all the other CPUs exit their critical sections. * * Note, however, that RCU callbacks are permitted to run concurrently * with RCU read-side critical sections. One way that this can happen * is via the following sequence of events: (1) CPU 0 enters an RCU * read-side critical section, (2) CPU 1 invokes call_rcu() to register * an RCU callback, (3) CPU 0 exits the RCU read-side critical section, * (4) CPU 2 enters a RCU read-side critical section, (5) the RCU * callback is invoked. This is legal, because the RCU read-side critical * section that was running concurrently with the call_rcu() (and which * therefore might be referencing something that the corresponding RCU * callback would free up) has completed before the corresponding * RCU callback is invoked. * * RCU read-side critical sections may be nested. Any deferred actions * will be deferred until the outermost RCU read-side critical section * completes. * * It is illegal to block while in an RCU read-side critical section. */ static inline void rcu_read_lock(void) { __rcu_read_lock(); __acquire(RCU); rcu_read_acquire(); } /* * So where is rcu_write_lock()? It does not exist, as there is no * way for writers to lock out RCU readers. This is a feature, not * a bug -- this property is what provides RCU's performance benefits. * Of course, writers must coordinate with each other. The normal * spinlock primitives work well for this, but any other technique may be * used as well. RCU does not care how the writers keep out of each * others' way, as long as they do so. */ /** * rcu_read_unlock - marks the end of an RCU read-side critical section. * * See rcu_read_lock() for more information. */ static inline void rcu_read_unlock(void) { rcu_read_release(); __release(RCU); __rcu_read_unlock(); } /** * rcu_read_lock_bh - mark the beginning of a softirq-only RCU critical section * * This is equivalent of rcu_read_lock(), but to be used when updates * are being done using call_rcu_bh(). Since call_rcu_bh() callbacks * consider completion of a softirq handler to be a quiescent state, * a process in RCU read-side critical section must be protected by * disabling softirqs. Read-side critical sections in interrupt context * can use just rcu_read_lock(). * */ static inline void rcu_read_lock_bh(void) { __rcu_read_lock_bh(); __acquire(RCU_BH); rcu_read_acquire_bh(); } /* * rcu_read_unlock_bh - marks the end of a softirq-only RCU critical section * * See rcu_read_lock_bh() for more information. */ static inline void rcu_read_unlock_bh(void) { rcu_read_release_bh(); __release(RCU_BH); __rcu_read_unlock_bh(); } /** * rcu_read_lock_sched - mark the beginning of a RCU-classic critical section * * Should be used with either * - synchronize_sched() * or * - call_rcu_sched() and rcu_barrier_sched() * on the write-side to insure proper synchronization. */ static inline void rcu_read_lock_sched(void) { preempt_disable(); __acquire(RCU_SCHED); rcu_read_acquire_sched(); } /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */ static inline notrace void rcu_read_lock_sched_notrace(void) { preempt_disable_notrace(); __acquire(RCU_SCHED); } /* * rcu_read_unlock_sched - marks the end of a RCU-classic critical section * * See rcu_read_lock_sched for more information. */ static inline void rcu_read_unlock_sched(void) { rcu_read_release_sched(); __release(RCU_SCHED); preempt_enable(); } /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */ static inline notrace void rcu_read_unlock_sched_notrace(void) { __release(RCU_SCHED); preempt_enable_notrace(); } /** * rcu_dereference_raw - fetch an RCU-protected pointer * * The caller must be within some flavor of RCU read-side critical * section, or must be otherwise preventing the pointer from changing, * for example, by holding an appropriate lock. This pointer may later * be safely dereferenced. It is the caller's responsibility to have * done the right thing, as this primitive does no checking of any kind. * * Inserts memory barriers on architectures that require them * (currently only the Alpha), and, more importantly, documents * exactly which pointers are protected by RCU. */ #define rcu_dereference_raw(p) ({ \ typeof(p) _________p1 = ACCESS_ONCE(p); \ smp_read_barrier_depends(); \ (_________p1); \ }) /** * rcu_dereference - fetch an RCU-protected pointer, checking for RCU * * Makes rcu_dereference_check() do the dirty work. */ #define rcu_dereference(p) \ rcu_dereference_check(p, rcu_read_lock_held()) /** * rcu_dereference_bh - fetch an RCU-protected pointer, checking for RCU-bh * * Makes rcu_dereference_check() do the dirty work. */ #define rcu_dereference_bh(p) \ rcu_dereference_check(p, rcu_read_lock_bh_held()) /** * rcu_dereference_sched - fetch RCU-protected pointer, checking for RCU-sched * * Makes rcu_dereference_check() do the dirty work. */ #define rcu_dereference_sched(p) \ rcu_dereference_check(p, rcu_read_lock_sched_held()) /** * rcu_assign_pointer - assign (publicize) a pointer to a newly * initialized structure that will be dereferenced by RCU read-side * critical sections. Returns the value assigned. * * Inserts memory barriers on architectures that require them * (pretty much all of them other than x86), and also prevents * the compiler from reordering the code that initializes the * structure after the pointer assignment. More importantly, this * call documents which pointers will be dereferenced by RCU read-side * code. */ #define rcu_assign_pointer(p, v) \ ({ \ if (!__builtin_constant_p(v) || \ ((v) != NULL)) \ smp_wmb(); \ (p) = (v); \ }) /* Infrastructure to implement the synchronize_() primitives. */ struct rcu_synchronize { struct rcu_head head; struct completion completion; }; extern void wakeme_after_rcu(struct rcu_head *head); /** * call_rcu - Queue an RCU callback for invocation after a grace period. * @head: structure to be used for queueing the RCU updates. * @func: actual update function to be invoked after the grace period * * The update function will be invoked some time after a full grace * period elapses, in other words after all currently executing RCU * read-side critical sections have completed. RCU read-side critical * sections are delimited by rcu_read_lock() and rcu_read_unlock(), * and may be nested. */ extern void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *head)); /** * call_rcu_bh - Queue an RCU for invocation after a quicker grace period. * @head: structure to be used for queueing the RCU updates. * @func: actual update function to be invoked after the grace period * * The update function will be invoked some time after a full grace * period elapses, in other words after all currently executing RCU * read-side critical sections have completed. call_rcu_bh() assumes * that the read-side critical sections end on completion of a softirq * handler. This means that read-side critical sections in process * context must not be interrupted by softirqs. This interface is to be * used when most of the read-side critical sections are in softirq context. * RCU read-side critical sections are delimited by : * - rcu_read_lock() and rcu_read_unlock(), if in interrupt context. * OR * - rcu_read_lock_bh() and rcu_read_unlock_bh(), if in process context. * These may be nested. */ extern void call_rcu_bh(struct rcu_head *head, void (*func)(struct rcu_head *head)); #endif /* __LINUX_RCUPDATE_H */